Dressing for dinner

D: It’s too hot to wear a t-shirt – I don’t want to wear one.
Me: You need to wear a top for dinner.
D: Why?
Me: Because everyone dresses nicely for dinner.
D: Why aren’t they allowed to dress horribly?
Me: That’s not what I mean – everyone just has to have a top on.
D: Are you allowed to dress funny?
Me: It depends who you’re sitting with and whether they’d find it funny.
D: What about crumbling up a pie and wearing it as a moustache – would that be OK?